The glass is pretty crusted, and I hate to get someone's hopes up who knows more about this than I do (most people,) but it appears that the tanks that I bought were made with low iron glass.

Looking at multiple panes more carefully, it appears that one of the three I picked up has 4 pieces that might be low iron (the front had been replaced at some point.) I just didn't have time to look at all of them carefully earlier and got excited.